In tires, gases such as air and nitrogen are usually charged therein in an inner pressure of about 250 to 350 kPa in terms of an absolute pressure to provide a skeleton part of the tire with a tension. The tension described above makes it possible to restore deformation caused by an applied force. However, if the tire is lacerated, the gas charged in the inside is leaked to the outside from the lacerated part to reduce the inner pressure of the tire down to an atmospheric pressure, and the tire is in a so-called punctured state.
In recent years, tires are requested to be enhanced more in performances as automobiles are increased in a driving speed. On the other hand, spare tires are desired to be unnecessary because of a reduction in a weight required to automobiles. Required are tires on which automobiles can continue to drive and move at least to a place making it possible to treat safely the tires even when the tires are punctured. Such the tires as described above make it possible to inhibit an inner pressure from being reduced and continuously drive and move without carrying out treatments such as prompt repair and exchange to a place where the tires can be treated safely even when the inner pressure is lowered to make the automobiles impossible to drive.
Tires in which a sealant material comprising a viscous rubber composition having a suitable fluidity is arranged in an inside are available as one of the tires described above. Applied is a technique in which when the tire is lacerated, the sealant material is inserted into the lacerated part by making use of an inner pressure of the tire to thereby seal the lacerated part and prevent the inner pressure from being reduced. In this connection, it depends on a retentivity and an adhering property of the sealant material whether or not the sealant material can function to seal the lacerated part.
When sharp foreign matters such as nails into a tire while driving, the sharp foreign matters stay in the tire in a certain case in a state in which foreign matters go through the tire without necessarily getting away soon. In the state described above, an inner pressure in the tire is not lowered immediately. Then, such a force as rubbing the foreign matters which stick into the tire is applied in the inside of the tire while driving. Accordingly, the foreign matters are rubbed against the tire on a contact face, and the contact face is abraded to some extent, whereby a gap is formed on the contact face. When the foreign matters are suddenly separated, the inner pressure is lowered, and the car cannot be driven in certain cases. In such the case, it depends on followability and a fluidity of the sealant material whether or not the lacerated part can be sealed by the sealant material.
Accordingly, first of all, the sealant material requires a suitable fluidity. The sealant material is characterized by containing a large amount of a plasticizer such as oils in the composition as compared with ordinary rubber compositions. In addition to requiring a large amount of a plasticizer, the rubber composition has to be adjusted in a balance with other blend components. Also, in addition thereto, a step different from that for conventional rubber compositions is required in a production step.
In particular, a rubber composition for a sealant material is characterized by containing a large amount of a plasticizer. When such the rubber composition as containing a large amount of a plasticizer is kneaded while heating for a long time, the plasticizer is volatilized to cause a loss. Produced is a vicious circle in which the plasticizer has to be further added in order to supplement the loss of the plasticizer. Also, as a matter of course, the problems of a deterioration in the working environment and a load applied onto the natural environment are involved therein.
It can be found in many cases that materials which are not subjected to cross-linking by sulfur are used in a composition unlike ordinary rubber compositions for tires. Used are materials showing a viscosity rather than such elastic to flexible rubber compositions which are rigidly cross-linked as used for ordinary tires. Accordingly, the rubber composition is turned into a sealant provided with a suitable viscosity by depolymerization by peroxide by heating at the same time in vulcanizing a peripheral rubber member rather than cross-linking to provide the rubber composition with a high molecular weight as is the case with patent document 1.